Tissue-engineering holds the promise of repairing or replacing failing organs to treat illness or improve and extend life expectancy. One of the principle methods behind tissue engineering involves growth of the relevant three-dimensional (3D) organ or tissue starting from dissociated cells and 3D porous matrices, known as scaffolds. The cells attach and colonize the scaffold to produce tissue constructs (Langer, R., Vacanti, J. P. (1993) Tissue engineering. Science 260: 920-926). Bioreactors are an important tool for successful clinical implementation of tissue-engineering and regenerative medicine strategies, as bioreactors are able to reliably reproduce physiological conditions in vitro. Improved bioreactors are needed to improve engineered tissue construct size, structure, mechanical properties, cellularity, and molecular composition to more closely resemble functional native tissues, and to maintain viability of harvested cells prior to their actual transplantation
One major challenge in tissue engineering that can be met by using a bioreactor is cell attachment to a 3D porous scaffold, herein referred to as ‘cell seeding’. To create an autologous implant starting from a biopsy of limited size and cells of limited expansion potential, the harvested cells should be seeded onto scaffolds with the highest possible efficiency. A spatially uniform distribution of cells throughout a 3D scaffold should provide the basis for homogeneous tissue generation, but it is challenging to disperse viable cells throughout 3D scaffolds having complex and diverse architectures.
A commonly used method of cell seeding is to add concentrated cells to a scaffold in a petri dish, but this ‘static seeding’ method is associated with low efficiency and spatially non-uniform cell distributions. Alternatively, cells can either be added to a magnetically stirred spinner flask in which scaffolds are threaded on needles and hence fixed in place or perfused through a cartridge in which a scaffold is fixed in place. However, previously developed cell seeding devices were associated with low efficiency and spatially non-uniform cell distributions.
Subsequent to cell seeding, sufficient transport of gases, nutrients and other molecules during the culture of large tissue constructs has been a primary obstacle in the field of tissue engineering. A cell culture device should provide high rates of gas exchange (for cell types with high oxygen requirements), relatively low working volumes (for cell types that require media supplementation with costly growth factors) and controllable levels of hydrodynamic shear (for cell types that are shear-sensitive).
A related challenge in the field of regenerative medicine that can be met by using a bioreactor is to maintain the viability of harvested cells prior to the time of their actual transplantation. Harvested cells typically die or lose their specialized phenotype (de-differentiate) when cultured in conventional petri dishes or spinner flasks. Moreover, shear stress, which is absent in petri dishes and present at high levels in spinner flasks, is required to support the oxygen and nutrient transport requirements of metabolically active cells, but high levels of shear stress can induce programmed cell death (apoptosis) and/or de-differentiation.
Current cell culture bioreactors suffer from several drawbacks. For example, typical cell culture bioreactor devices require two distinct system components: one to provide gas exchange and another to provide perfusion. The requirement for two separate components renders the devices bulky and cumbersome. Additionally, existing bioreactor devices work in two distinct phases: one device is required for the cell seeding phase and a second device is required for the cell culture phase. Lastly, the majority of the existing bioreactor devices developed for cell seeding and culture are of limited use in a commercial setting, due to complexity of the required components, e.g. multi-channel peristaltic pumps, bi-directional syringe pumps or vacuum pumps combined with multiple sensors and solenoid valves.
Therefore, it is an objective of the invention to provide an integrated cell culture bioreactor suitable for cell seeding and cell culture for the production of tissue engineered constructs.
It is a further objective of the invention to provide methods for producing tissue constructs using a single, integrated bioreactor for cell seeding and cell culture.
It is a further objective of the invention to provide a cell culture bioreactor that combines effective mass transport of gases, nutrients, and regulatory molecules in the context of a single, integrated and commercially applicable device.
It is a further objective of the invention to provide a method and cell culture apparatus that can provide sufficient transport of gases, nutrients and other molecules during the culture of tissue constructs greater than 200 μm one dimension.
It is still another objective of the invention to provide an integrated cell culture bioreactor suitable for maintaining the viability of harvested cells prior to the time of their actual transplantation.